This invention relates to arrays of interconnected semiconductor devices such as photovoltaic cells for direct conversion of sunlight into electrical energy. It is known that large area solar cell arrays can be produced on glass and relatively thick metal substrates. For example, such arrays may be produced by depositing an amorphous silicon alloy on coils of metal strips that may be unrolled for deposition and rolled again after the deposition. See U.S. Pat. Nos. 4,410,558 for Continuous Amorphous Solar Cell Production System; 4,419,530 for Solar Cell and Method of Producing Same; 4,443,652 for Electrically Interconnected Large Area Photovoltaic Cells and Method of Producing Said Cells; and 4,485,125 for Method of Continuously Producing Tandem Amorphous Photovoltaic Cells, the disclosures of which are incorporated herein by reference. It is also known that amorphous silicon can be deposited on thin foils of nickel prepared by an electroforming technique. See U.S. Pat. No. 4,530,739 for Electroplated Substrate, which is incorporated herein by reference. It has also been reported that amorphous silicon may be deposited by glow discharge on narrow plastic sheets 15 micrometers in thickness that are continuously drawn through a low pressure deposition chamber. See U.S. Pat. No. 4,341,588.
Various methods of forming electrically interconnected arrays of small-area photovoltaic cells from relatively large areas of deposited photoresponsive semiconducting materials are known. For example, in my U.S. Pat. No. 4,514,579 and incorporated herein by reference, I have disclosed a "checkerboard" array of series-connected rows of photovoltaic cells in which the rows are electrically connected in parallel. Other series-connected arrays are disclosed in U.S. Pat. No. 4,245,386 to Kausche et al.
Traditionally, photovoltaic cells have been fabricated on a substrate that may be electrically conducting or may be an insulator. Typically, the substrate is the thickest member of a cell or an array of cells and contributes most of the weight to the cell or array. In applications where weight is an important or critical factor, such as extraterrestrial or certain consumer uses, it is desirable to minimize the weight of a photovoltaic array, which means minimizing the weight of the substrate. A particularly lightweight, interconnected array of devices could be made if the substrate were made unconventionally thin or a conventional substrate were eliminated entirely. However, use of a very thin substrate or no conventional substrate at all results in substantial difficulty in handling a large area of semiconductor material and forming it into an interconnected array.
In the invention, the problems of processing arrays of cells with an unconventionally thin substrate or without a conventional substrate are solved. Various alternative methods for producing such arrays have been developed. Arrays according to the invention are flexible and lightweight, permitting them to be rolled for storage in a relatively small volume. Because the weight of the inventive photovoltaic arrays is small, the specific power, i.e. output power divided by weight, is very large and provides an apt factor for measuring performance. It is also possible according to the invention to maximize the specific power of a photovoltaic array by eliminating a conventional substrate entirely.